Hmmm i used some code like this when i tried to write some diagnostic roms for testing 'dead' motherboards... most 'dead' boards where the result of memmory problems in the first 64k of ram.. (untill thats been tested as good you cant generally init the vga class cards by there bios entry point). what i did was to init an original mda card from ibm and use the bottem two lines of the display as memmory. (if thay were displayed it looked good going through my diags with the stack sitting in display memmory) however the speed penalty for useing a 486 cpu was drastic in the extreme it would take hours to do a reasnoble ram test.
On Wed, 11 Mar 1998, Pascal Dornier wrote:
The MDA cards require absolutely no setup. They display text from the
moment
the power goes on. I suspect older [CEV]GA cards will be similar.
Not correct, you need to initialize the 6845 CRTC. Pardon the grotty formatting.
; ; Init Hercules card ; cld mov al,#$21 ;disable video mov dx,#$03b8 out dx,al mov si,#herctext ;set text mode mov bl,#0 mov dx,#$03b4 hercloop mov al,bl out dx,al inc dx cs: lods.b out dx,al dec dx inc bx cmp bl,#16 jb hercloop mov al,#$29 ;enable video mov dx,#$3b8 out dx,al mov ax,#$b000 ;clear screen mov es,ax mov ax,#vidfill mov cx,#2000 mov di,#0 rep stos jmp hercend ; ; Hercules text mode settings ; herctext B $61,$50,$52,$0F,$19,$06,$19,$19 ; mode 7 B $02,$0D,$0B,$0C,$00,$00,$00,$00 hercend
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